An integrated circuit typically includes transistors and other devices formed on a semiconductor substrate. A capacitor may be provided as part of an integrated circuit by forming a first conductive electrode, a dielectric layer on the first electrode, and a second conductive electrode on the dielectric layer. Such capacitors are commonly used in memory cells for DRAM devices, for example, as well as in analog-to-digital converters and other circuits.
As disclosed in U.S. Pat. No. 5,910,880 to DeBoer et al., for example, tantalum pentoxide (Ta.sub.2 O.sub.5) is a desired material for a capacitor dielectric because of its relatively high dielectric constant of about 25. In comparison, silicon nitride has a dielectric constant of about 8, and silicon dioxide has a dielectric constant of about 4. The high dielectric constant of tantalum pentoxide allows a thinner layer of the material to be used between the electrodes to achieve the same capacitance as using other lower dielectric constant materials.
A typical construction of such a capacitor includes a first or lower electrode of polycrystalline silicon. A first barrier layer of silicon nitride is typically provided to protect the polycrystalline silicon from forming into silicon dioxide and to prevent diffusion as the tantalum pentoxide is deposited thereon. A second barrier layer of titanium nitride or tungsten nitride may be deposited over the tantalum pentoxide prior to forming the polycrystalline silicon or metal layer of the upper electrode.
U.S. Pat. No. 5,622,888 to Sekine et al. discloses making a DRAM capacitor also using tantalum pentoxide. A layer of tungsten is sputter deposited on a polysilicon lower electrode. The tantalum pentoxide is deposited by chemical vapor deposition (CVD) at a temperature in a range of 300 to 600.degree. C. Unfortunately, the higher temperatures may have a tendency to oxidize the tungsten. Thereafter, the tantalum pentoxide is densified by a plasma using an oxygen gas at a temperature ranging from 200 to 600.degree. C. An upper tungsten electrode is formed on the tantalum pentoxide.
Despite continuing development in the field of integrated circuit capacitors using tantalum pentoxide as the dielectric, there still exists a need to further develop the manufacturing process to produce such capacitors having relatively high capacitance values and other desirable properties.